Forget recovery, acceptance, moving on. Just getting through the day is the task at hand in "Rabbit Hole," John Cameron Mitchell's film of the Pulitzer Prize-winning play by David Lindsay-Abaire. Nicole Kidman gives one of the best performances of her career as a grieving mother who will deal with the death of her 4-year-old son on her own terms, thank you very much.

Aaron Eckhart also is outstanding as her husband, trying to grieve in his own separate way. The film is quiet, patient, allowing for lived-in performances that get at the enormous change in the characters' lives. If it sounds like difficult material, it is - although we don't see the death of their son (the film takes place a few months afterward), we certainly see its effects. But the film is not without humor, some of it brought to bear in unusual places - a meeting of grief survivors, for example, or a birthday party at a bowling alley.

Becca (Kidman) gave up her lucrative job when her son was born. Howie (Eckhart) still goes off to work, returning each night to their nice suburban home, where he has dinner, engages in banal conversation with Becca and, later, watches home movies of their son, picking at a scab he will not allow to heal. He needs the survivors' support group; Becca ridicules it, not as a dig at Howie but as something that holds people captive in their mourning, revisiting it, unwilling or unable to move on. As you would imagine, this is not ideal for their relationship. Howie befriends Gaby (Sandra Oh), who has been attending the sessions for years.

Becca, meanwhile, putters in her garden and navigates the tricky relationships with her mother, Nat (Dianne Wiest, excellent), who has endured her own tragedies, and sister Izzy (Tammy Blanchard), who is, to Becca's consternation, pregnant. Then one day Becca runs across Jason (Miles Teller), the teenage boy who was driving the car that hit her son (who had chased his dog into the street). It's clumsy, of course, at times almost stalker-ish, but it also reveals the damage inflicted upon Jason as well. (The film's title comes from a graphic novel Jason has created, dealing with alternate universes and lives.)

Teller nails Jason's awkwardness and guilt; like everyone else, he wants to move on but can't. Wiest gives Nat a certain battiness that at times is charming, at times maddening (especially to Becca). Eckhart has a habit of playing opposite actors who do career-best work (Julia Roberts in "Erin Brocko- vich," Heath Ledger in "The Dark Night"). It can be thankless work. It shouldn't be. Here he brings both pain and humor to a challenging part, enhancing what Kidman does, never overshadowing it.

And there's no question that it's ultimately Kidman's film. Movies made from plays can be tricky. As in "Doubt," for instance, the cast tends to want to play to the back row. Kidman does none of that. She draws us into Becca's damaged world in small ways. She and Mitchell trust that the audience will be patient as the character and the story develop. Both do, and thanks to Kidman's remarkably naturalistic performance, it's worth the wait.